1. Field of the Invention
The present invention relates to a method for producing a semiconductor device, and more particularly to a method for producing a semiconductor device such as a light-emitting display device displaying numbers, etc. by means of a light-emitting device, a photointerrupter, a leadless IC, and a number of light-emitting diodes (LEDs). More specifically, the present invention relates to a method for producing a semiconductor device and a light-emitting display device including a circuit board made of a metallic substrate or a resin substrate such as that made of glass epoxy resin and molded interconnection device (MID) on which a functional element such as an LED and an IC is provided so as to be sealed with a sealing resin.
2. Description of the Related Art
In recent years, micro light-emitting devices with a size of 1 mm square having a reflective plate have been developed, which use a circuit board provided with a reflective function, made of a metallic substrate or a resin substrate such as that made of glass epoxy resin and an MID. Such light-emitting devices having a reflective plate have a configuration in which a cavity is formed on a circuit board with a reflective function and an LED is mounted in the cavity so as to be sealed therein with a resin such as a light-transparent thermosetting resin. The inner peripheral surface of the cavity functions as a reflective plate, so that light emitted from the LED in the cavity passes through the sealing resin and is reflected from the inner peripheral surface of the cavity.
When such micro light-emitting devices having a reflective plate are produced, a multi-cavity circuit board made of one MID provided with a number of cavities in a matrix is used so as to produce a number of light-emitting devices at the same time.
The above-mentioned micro light-emitting device using a multi-cavity circuit board is produced as follows:
First, LEDs are respectively mounted in the cavities by die bonding and wire bonding. Then, a sealing resin in a liquid state or in a molten state is used to fill the respective cavities. The filled resin is cured, whereby a number of light-emitting devices are produced at the same time. The respective cavities are generally filled with the sealing resin by cast molding, injection molding, or transfer molding.
A method for filling the cavity with the sealing resin by the conventional cast molding will be described with reference to FIGS. 25A to 25F.
(1) As shown in FIG. 25A, a main agent 91a and a curing agent 91b are mixed to prepare a sealing resin 91 in a liquid state. As the sealing resin 91, a thermosetting resin can be generally used; in particular, epoxy resin is preferably used. (2) As shown in FIG. 25B, the sealing resin 91 thus obtained is sufficiently stirred. (3) As shown in FIG. 25C, the sealing resin 91 is deaerated in a vacuum oven 92. (4) As shown in FIG. 25D, the deaerated sealing resin is poured into a molding machine 93. (5) As shown in FIG. 25E, a multi-cavity circuit board 94 on which a number of cavities 94a are formed in a matrix and an LED has been mounted in each cavity 94a by die bonding and wire bonding is placed in the molding machine 93. Then, the sealing resin 91 in a liquid state is filled in each cavity 94a by a dispenser 93a. The dispenser 93a can be an air pressure type, a tubing type, a micro-gear pump type, etc. (6) As shown in FIG. 25F, the multi-cavity circuit board 94 is heated by an oven 95 so as to cure the sealing resin 91 in a liquid state in each cavity 94a.
The multi-cavity circuit board 94 filled with the sealing resin 91 is divided into a predetermined number of cavities 94a, whereby micro light-emitting devices with a reflective plate, in which the LED is sealed in the cavity on the circuit board with the sealing resin 91, are produced.
A method for filling a sealing resin by the conventional injection molding will be described with reference to FIGS. 26A to 26F.
(1) As shown in FIG. 26E, a multi-cavity circuit board 96 with a number of cavities 96a provided in a matrix is used. The multi-cavity circuit board 96 has groove portions 96b provided so as to form separate rows of connected cavities 96a arranged side by side on its surface. (2) As shown in FIG. 26A, the multi-cavity circuit board 96 is placed on a lower mold 97b of a mold 97 for injection molding, an upper mold 97a thereof is attached to the lower mold 97b, and the mold 97 is clamped. (3) As shown in FIG. 26B, a tip end of an injection cylinder 97d is inserted into a nozzle portion 97c provided in the mold 97. (4) A thermoplastic resin in a molten state is supplied into the injection cylinder 97d. As shown in FIG. 26C, the thermoplastic resin is injected into the mold 97 through the nozzle portion 97c and a gate 100 while being pressed by an injection plunger 97e. (5) The molten resin injected into the mold 97 fills each cavity 96a through each groove portion 96b of the multi-cavity circuit board 96. The thermoplastic resin is solidified by forced cooling or by being allowed to cool to room temperature. After the molten resin is solidified in each cavity 96a, the upper mold 97a is detached from the lower mold 97b, as shown in FIG. 26D. (6) As shown in FIG. 26E, the multi-cavity circuit board 96 with each cavity 96a filled with the solidified resin is taken out of the lower mold 97b. (7) As shown in FIG. 26F, the gate 100 is detached from the multi-cavity circuit board 96. Thus, the multi-cavity circuit board 96 with each cavity 96a filled with the thermoplastic sealing resin is obtained. The multi-cavity circuit board 96 is divided into the respective cavities 96a, whereby micro light-emitting devices with a reflective plate can be produced.
A method for filling a sealing resin by the conventional transfer molding will be described with reference to FIGS. 27A to 27G.
(1) As shown in FIG. 27E, in the same way as in the above-mentioned injection molding, a multi-cavity circuit board 96 is used, on which a number of cavities 96a are formed in a matrix and groove portions 96b are provided so as to connect the respective cavities 96a into separate rows arranged side by side. (2) As shown in FIG. 27A, the multi-cavity circuit board 96 is placed on a lower mold 98b of a mold 98 for transfer molding, an upper mold 98a thereof is attached to the lower mold 98b, and the mold 98 is clamped. The upper mold 98a has a heating chamber 98c for heating a sealing resin to be charged thereinto. (3) As shown in FIG. 27B, a thermosetting sealing resin 99 which has been B-staged, and plasticized if required, is charged into the heating chamber 98c. (4) As shown in FIG. 27C, the sealing resin 99 is melted in the heating chamber 98c and injected into each cavity 96a of the multi-cavity circuit board 96 through a gate 100 under pressure. (5) The sealing resin is primary-cured in the mold 98 (i.e., in the cavities 98a). Then, as shown in FIG. 27D, the upper mold 98a is detached from the lower mold 98b. (6) As shown in FIG. 27E, the multi-cavity circuit board 96 is taken out of the lower mold 98b. (7) As shown in FIG. 27F, the gate 100 is detached from the multi-cavity circuit board 96. (8) As shown in FIG. 27G, the multi-cavity circuit board 96 is heated in an oven 95 so as to secondary-cure the sealing resin 99 in each cavity 96a. Thus, the multi-cavity circuit board 96 with each cavity 96a filled with the thermosetting sealing resin is obtained. The multi-cavity circuit board 96 is divided into the respective cavities 96a, whereby micro light-emitting devices with a reflective plate can be produced.
In any of the above-mentioned methods, by dividing the multi-cavity circuit board 96 into a predetermined number of groups of cavities instead of dividing it into a predetermined number of cavities 96a, a dot-matrix type light-emitting display device capable of displaying numbers, etc. in a variable manner can be produced.
Alternatively, light-emitting devices can be produced by filling with a sealing resin without using the above-described multi-cavity circuit board provided with a plurality of cavities. For example, micro light-emitting devices are produced by using a flat circuit board or a lead frame. Such micro light-emitting devices can be produced by potting, dipping, etc. According to potting, a plurality of LEDs are provided in a matrix on a flat circuit board or a lead frame by die bonding and wire bonding, and a liquid sealing resin (e.g., epoxy resin) is dipped onto each LED so as to be cured, whereby each LED is sealed. According to dipping, a flat circuit board or a lead frame provided with LEDs is soaked into a liquid sealing resin (e.g., epoxy resin) and pulled up; thereafter, excess sealing resin adhered to the flat circuit board or the lead frame is removed with a spinner and the remaining sealing resin adhered to the flat circuit board or the lead frame is cured.
In the case of producing light-emitting devices by using a flat circuit board or a lead frame instead of a multi-cavity circuit board, transfer molding or injection molding can be adopted.
In the case where dot-matrix type light-emitting display devices having a plurality of LEDs are produced, a flat circuit board can also be used. In this case, a reflective plate having openings is put on a flat circuit board on which a plurality of LEDs are provided in a matrix by die bonding and wire bonding. The reflective plate has as many openings as there are of the LEDs and is composed of a metal or resin molding. When the reflective plate is put on the flat circuit board, each LED on the flat circuit board is contained by each opening in the reflective plate. Each LED and wire on the flat circuit board are coated with a protecting resin such as silicone resin and a liquid thermosetting resin by using a brush or sprayed with a protecting resin such as silicone resin and a liquid thermosetting resin by using a spray or a nozzle. Thereafter, each LED and wire are cured so as to be protected.
According to this method, in order to render light emitted from the LEDs uniform, a reflective plate is fixed onto the flat circuit board and thereafter, a dispersion sheet is attached to the surface of the reflective plate.
Hereinafter, problems involved in the above-mentioned conventional methods will be described.
In the casting molding using the multi-cavity circuit board 94, there is a possibility that the viscosity of the sealing resin to be filled in each cavity 94a changes with time in the dispenser 93a. For this reason, the dispenser 93a should control a discharge amount with high precision so that a predetermined amount of sealing resin can be poured into each cavity 94a even if the viscosity of the sealing resin in the dispenser 93a changes. In particular, in the case where micro light-emitting devices with a reflective plate are produced, the amount of the sealing resin to be poured into each cavity 96a is as small as 0.001 cc, so that a dispenser capable of controlling a discharge amount with higher precision is required.
In order to control the discharge amount in accordance with the change in viscosity of the sealing resin, the amount of the sealing resin to be poured into the dispenser 93a should be made small. However, if the amount of the sealing resin to be poured into the dispenser 93a is decreased, the sealing resin in the dispenser 93a is consumed within a short period of time, which makes it necessary to pour the sealing resin into the dispenser 93a a number of times, resulting in the remarkable decrease in working efficiency.
Alternatively, in order to control the discharge amount in accordance with the change in viscosity of the sealing resin, it is important to efficiently pour the sealing resin into each cavity 94a of the multi-cavity circuit board 94. For this purpose, there should be as many dispensers 93a as cavities 94a or the combination of an X-Y table capable of being positioned with high precision and one or more dispensers 93a should be provided. However, providing such dispensers necessitates enlarged and complicated equipment, which is not preferably in terms of cost efficiency.
Furthermore, while the sealing resin is cured in each cavity 94a, components with a low boiling point contained in the liquid sealing resin evaporate. Thus, the smaller the capacity of each cavity 94a is, the larger the proportion of the evaporating components with regard to the capacity of each cavity 94a is. This causes a large change in the amount of the sealing resin which remains to be cured in the cavities 94a, leading to the possibility that a predetermined amount of the sealing resin is not cured in each cavity 94a. In some cases, micro light-emitting devices with a reflective plate, having desired characteristics, cannot be obtained.
As described above, according to the filling method using the casting molding, an expensive and complicated dispenser system is required, which causes problems such as a longer resin supply time and the change in characteristics of the resultant light-emitting devices.
According to the filling methods using the injection molding and the transfer molding, the groove portions 96b connecting the respective cavities 96a into separate rows arranged side by side should be provided on the multi-cavity circuit board 96. In the case of producing light-emitting devices using the multi-cavity circuit board 96 provided with the groove portions 96b, the sealing resin is filled to be cured in the groove portions 96b as well as in the cavities 96a. This causes light emitted from the LEDs to be output through the sealing resin in the groove portions 96b. As a result, there arises a problem such as the decrease in luminance due to light leakage, i.e., the generation of stray light, leading to the decrease in quality of the light-emitting devices.
Furthermore, according to the injection molding, a mold and a molding machine capable of injecting a molten resin into each cavity 96a are required. However, in order that the molten resin is injected so as to fill each cavity 96a completely without mixing air bubbles therein, a mold which is precisely processed and a molding machine capable of injecting the molten resin at a high pressure are required. This increases the equipment expenses, leading to the degradation of cost efficiency. In order to fill the molten resin so as to fill each cavity 96a completely without using such an expensive mold and molding machine, decreasing the number of the cavities 96a in the multi-layer cavity circuit board 96 will suffice; however, the production efficiency is remarkably decreased.
According to the potting method and the dipping method, a liquid sealing resin should be prepared so as to have a desired characteristic and configuration and be cured. Thus, the management of a process is very complicated. Furthermore, according to these methods, since the sealing resin is not filled in containers such as cavities with a predetermined shape, it is very difficult to obtain cured sealing resin in a uniform shape.
In the injection molding or the transfer molding using a flat circuit board or a lead frame, an expensive mold and molding machine are required in the same way as in the case using a multi-cavity circuit board. Furthermore, passages for injecting a sealing resin should be formed in the flat circuit board. Particularly in the injection molding, when using a liquid thermosetting resin as a sealing resin, the viscosity of the sealing resin immediately after being injected into the mold decreases dramatically because the sealing resin is heated in the mold. For this reason, there is a possibility that the sealing resin flows into portions where the sealing resin is not necessary, such as the reverse face of the flat circuit board.
In the case where the flat circuit board is coated with a protecting resin with a brush during the production of dot-matrix type light-emitting display devices, there is a possibility of lead wires such as gold wires bonded to each LED by wire bonding coming into contact with the brush thereby to deform or to peel off. Thus, close attention should be paid so as to prevent the lead wires from deforming or peeling off, which decreases the production efficiency. In the case where a liquid protecting resin is sprayed by a spray or a nozzle, there is a possibility that the protecting resin is coated onto portions other than a circuit board, leading to the contamination of work environment.
Furthermore, the method for producing light-emitting display devices using a flat circuit board needs the steps of fixing a reflective plate onto the flat circuit board so that the reflective plate is not detached therefrom and of attaching a dispersion sheet to the reflective plate. This further decreases the production efficiency.
As described above, the conventional methods have the respective problems.